Prince William had no complaints about his only daughter when she was still in diapers. “Charlotte is very easy,” the Prince of Wales, 41, said of his middle child, “but all the fathers say, ‘Just you wait, when you get to 9, 10, 11, they go crazy.’ I’m looking forward to it… there will be some drama.”

So far, so good. Charlotte’s only 8 yet has shown remarkable poise and maturity as she approaches her tween years,  a royal source tells Life & Style exclusively. “Charlotte had really been a daddy’s girl, but now that she’s getting older, she leans on her mom more,” reveals the source, who notes that Princess Kate, 41, and her little girl “have a close and very sweet bond, much like Kate and her own mother,” Carole Middleton, 68. “Kate loves being so tight with her daughter and makes sure she’s not only teaching and guiding her, but also ensuring they have a lot of fun together!”

That includes making time for one-on-one adventures with her mini-me. “They’ll have secret sleepovers at London hotels, just the two of them, and order room service and watch TV,” says the source. “They love going to the theater, too. Kate took Charlotte and her friends to see the ballet Cinderella at the Royal Opera House in London last year, and they all had the best time.”

Mother and daughter also connect over crafts — like making homemade gifts for neighbors for the holidays — animals and clothes. “They’re on dog duty for their cocker spaniel, Orla, more than anyone else in the family,” says the source. “And Charlotte loves watching Kate get ready for events. They can’t really go to stores to shop together, but they’re always checking out fashion on Kate’s iPad.”

Still, the Cambridge girls would both trade fancy dresses and tiaras for athletic gear any day. “[Kate] regularly plays rugby in the back garden with the children — she plays all sports with them,” Nigel Gillingham, president of the Rugby Football Union, of which Kate is patron, revealed in June of the Princess of Wales and her brood — which also includes Prince George, 10, and Prince Louis, 5.

He noted that Charlotte, in particular, takes after her “very competitive” mother. William has described Charlotte as a “budding star” in soccer, but last summer, the little girl herself reportedly revealed “gymnastics” was her sport of choice. Kate, says the source, “sees a lot of herself in Charlotte, who never sits on the sidelines. She always wants to jump right in.”

Lately, Charlotte has had several opportunities to show just how ready for duty she is. “This summer is Charlotte’s coming out party, in a way,” says the source, pointing to the impeccable behavior, confidence and penchant for charming crowds she’s displayed as she’s stepped out with her parents in recent weeks. “It wouldn’t be surprising if we start to see Charlotte by Kate’s side at more events.” As for George and Louis? They won’t complain about Charlotte getting special attention, insists the source, because “she actually enjoys the walkabouts, while they’re happy to stay home.”

Though duty calls, Kate is excited to spend even more time with Charlotte and her brothers during their school break as the family prepares to escape on a summer vacation, with Mustique and Scotland among their usual destinations. “Kate’s pretty strict during the school year — with homework, afterschool activities and early bedtimes,” says the source. “But she sees the summer as a time when they can let go, a little bit, of their rules and just enjoy each other’s company.”